The present invention relates to optical pickups for reading data on optical disks.
U.S. Pat. No. 4,757,197 and U.S. Pat. No. 4,731,772 of this inventor disclosed the construction of a hybrid device and the use of the hybrid device and a hologram lens in an optical pickup.
FIG. 1 shows a hybrid device 100 from U.S. Pat. No. 4,757,197 containing a power monitor photodetector 101 on the back side of a laser diode chip 103. Laser diode chip 103 is mounted on a heatsink 107. A four segment photodetector 105 is mounted on the top of heatsink 107. Electrical connections to the photodetectors and the laser chip are accomplished by wires bonded from the devices to the pins 109-116 of a header structure.
FIG. 2 shows one of the constructions of an optical pickup disclosed in U.S. Pat. No. 4,731,772. The hybrid device 100 of FIG. 1 provides the light source and the detection mechanism for the pickup. A hologram lens 74 fulfills the functions of a beamsplitter and other lenses in a conventional optical pickup. The position of hologram lens 74 can either before or after a collimating lens 72. In another embodiment the collimating lens can be eliminated.
Hybrid device 100, collimating lens 72 and hologram lens 74 form a laser pen 84. A laser beam 70 from device 100 passes through these lenses to a focus and tracking actuator 82. Actuator 82 moves an objective lens 76 with magnetic coils 80 to focus the laser beam on a media 78.
FIG. 3 shows a conventional optical pickup used in a computer storage system. A high power laser diode 300 with output power of 30 mW or more is collimated by a lens 302. The laser diode is arranged so that the polarization of the laser is parallel to the plane of incidence of the beamsplitter (i.e. p-polarized). A polarization beam splitter 304 transmits nearly 100 percent of the collimated laser output through a quarterwave plate 306 to an objective lens 308. The returned beam after reflecting off a disc 310 passes through the quarterwave plate 306 again. As a result, the polarization orientation of the returned beam is rotated 90 degrees from its original polarization direction, and it is reflected by the beamsplitter towards a detector 314. Because the laser diode 300 is used for both reading (low power) and writing (high power), the servo signal at the detector fluctuates widely depending on the power output of the laser diode 300. As a result special electronics are used to normalize the output signals from the photodetectors.
U.S. Pat. No. 4,918,675 of this inventor shows an optical pick-up for a magneto optic medium. P-polarized light is provided from a hybrid laser detector through a beam splitter to the medium and is reflected back to the detector in the hybrid for servo purposes. Where a data value has been written, the reflected light will be partially s-polarized, and will be reflected by the beam splitter to a separate detector. The signal detected is small because only a small component is s-polarized. In addition, the signal is made smaller because originally the beam passes through a hologram lens which is used for servo tracking, thus reducing the intensity of the beam.